The invention concerns a heating or cooling plate for press installations, in particular, a dual belt press.
Heating or cooling-type press plates are disclosed in German Pat. No. 27 29 559 wherein steel belts carrying the material to be pressed travel between the press plates while being supported by a plurality of rotary press rolls. The latter serve to reduce friction between the belts and the press plates, as well as to transfer heat from the press plates to the steel belts and from there to material being pressed (or, inversely, to remove heat from the material being pressed, if the plate is a cooling plate). A disadvantage of such heated or cooled dual belt presses involves the fact that the heating or cooling plates are thermally deformed by different amounts on their two sides, due to the differential heat transfer on such sides, especially if there are large differences in temperature between the material being pressed and the heating (or cooling) plate. This results in a non-uniform thickness of the material being pressed.
Accordingly, in some systems, the press plates are supported relative to the upper and lower belts of the adjacent press stand on spacing strips, which strips may be heated so that as a result of differential thermal expansions of the spacing pieces, any thermal deformation of the press plates, or any manufacturing tolerances of the press, can be compensated for.
In other systems, such as those disclosed in German Printed Application No. 11 54 255 and German Pat. No. 20 36 926, there is provided the possibility of differentially heating the upper and lower belt of the press stand of multiple platen presses, in order to obtain flat contact surfaces for the material being pressed. However, such systems have the disadvantage that the mass to be heated is very large, so that the inertia of these presses is too high for the rapid equalization of potential variations in thickness.
All of the known systems require relatively complicated heating installations operating under differential temperature controls in order to obtain the required desired.
A press disclosed in German Pat. No. 12 36 939 includes a heating plate for discontinuous pressing operations, the plate having a two layer structure. The two layers comprise a heating plate layer mounted on a support plate layer by means of threaded bolts. The bolts extend through bores in the layers and engage guides. Each guide comprises two parallel ribs which form a slot directed toward the center of the heating plate. The heating plate may therefore shift relative to the support plate due to thermal expansion and contraction. In such a configuration, the heating plate is not located, as in the case of dual belt presses, opposite a moving steel belt supported against the heating plate by a revolving roll chain, whereby frictional forces are to be reduced. The heating plate would be undesirably deformed in a dual belt press by the shear forces applied by the rolls running over the heating plate.
It is an object of the invention to provide a heating or cooling plate of the afore-mentioned type for a dual belt press so that within the plate the deformation resulting from differential thermal expansion will remain as low as possible, wherein the forces applied by the support roll chains will not lead to interference with the heating plate.